Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
07-19-2009, 08:22 PM   #1
Veteran Member
mtroute's Avatar

Join Date: Jun 2009
Location: Portland OR
Posts: 532
Strange lights with long exposures

I tried out some long exposures over the weekend and saw some strange things that seem to me to be hardware problems. Can anyone explain the purple light in the same exact location on 3 separate exposures?

Example one, look along the top of the image.


Aperture: ƒ/4
Shutter Speed: 3.71 mins
ISO: 1600

Example 2, same location in the frame but not quite as severe.


Aperture: ƒ/4
Shutter Speed: 133.4s
ISO: 1600

And the 3rd example:


Aperture: ƒ/5.6
Shutter Speed: 426.5s
ISO: 800

During the star exposures there was NO other light source and this location is in the Willamette national forest far from any city lights. The creek picture was lit with a single 4w fluorescent flashlight located about 20 feet to the right of the camera.

All pictures were taken in Bulb mode with the camera laying on a wooden bridge (not perfectly still however) with me holding the shutter button (even less still) it was an impromptu shoot.

Ideas?

07-19-2009, 08:36 PM   #2
Ash
Community Manager
Loyal Site Supporter
Ash's Avatar

Join Date: Mar 2007
Location: Toowoomba, Queensland
Photos: Gallery | Albums
Posts: 22,678
It does seem these artifacts are sensor or lens dependent. Were all these taken with the same lens? If so, try again with another lens to see if you get the same result. If so, I'd say it's from sensor heat. I've seen similar effects on my K10D, but not always - usually as a result of some extraneous light source trickling through the lens, but I've not yet tried it on my K20D.

Let us know how you go with that.
07-19-2009, 08:48 PM   #3
Veteran Member
mtroute's Avatar

Join Date: Jun 2009
Location: Portland OR
Posts: 532
Original Poster
Yes they were all taken with the DA 18-55mm 3.5-5.6.
07-19-2009, 10:18 PM   #4
Senior Member




Join Date: Jul 2009
Location: fort worth tx
Photos: Gallery
Posts: 107
could this be light leaking in from the eye veiw finder?

07-19-2009, 11:32 PM   #5
Veteran Member
inferno10's Avatar

Join Date: Feb 2007
Location: San Francisco, California
Posts: 342
QuoteOriginally posted by mtroute Quote
I tried out some long exposures over the weekend and saw some strange things that seem to me to be hardware problems. Can anyone explain the purple light in the same exact location on 3 separate exposures?
Off-camera UFOs!

EDIT: Here's another thing to test. Try making a long exposure with the lens cap and viewfinder cap on in a dark room, and see if you get the purple splotches. If you do, then it's most likely heat from the sensor affecting the image. If not, try without the viewfinder cap; if you get splotches, then it's the viewfinder leaking.

- Jason

Last edited by inferno10; 07-19-2009 at 11:37 PM.
07-19-2009, 11:51 PM   #6
New Member




Join Date: Dec 2007
Location: Germany
Posts: 11
That noise is called amplifier-noise...
It comes from the amplifier sitting next to the sensor. I got that quite strong on my Nikon CP8800 but on the K10d it is much less of a problem.
I just saw this yesterday after a 1300 seconds exposure at iso 100.

If you increase iso the purple noise will also increase.
07-20-2009, 12:10 AM   #7
Veteran Member




Join Date: Jan 2009
Location: Brisbane
Photos: Gallery
Posts: 1,421
my guess would be heat related noise too, 3 mins + at ISO 1600 is a lot!

nice shot apart from the purple bits though!
07-20-2009, 12:50 AM   #8
Pentaxian




Join Date: Jun 2009
Location: GMT +10
Photos: Albums
Posts: 10,576
I've taken a few thousand shots with my K200D and only seen this two times, thankfully.

I took a series of 50 or more night exposures around town the other day using a M series 50mm 1.7 at 800 and lower ISO w. my K200D. Exactly the same sort of purple flare showed up in only one of those photos (3.5 second exposure), in only one spot in the very top left of frame.

One other occassion I saw two of those purple patches in the lower area of a shot @1600 ISo 1/15th of a second using the same 500mm 1.7 wide open.

The lack of consistency in the purple patches showing up makes me suspect light leakage rather than sensor issues. Next time I will take along my viewfinder cover.

Attached Images
   
07-20-2009, 01:01 AM   #9
Pentaxian
LeDave's Avatar

Join Date: Jun 2009
Location: Minneapolis - St. Paul
Photos: Gallery
Posts: 2,895
I have these a couple of times shooting with my Pentax K-m/K2000. I thought it was my filter problem because I'm using a Hoya UV S-HMC 52mm. The lenses I shoot with is the kit lens DA L 18-55mm AL.
07-20-2009, 02:47 AM   #10
New Member




Join Date: Dec 2007
Location: Germany
Posts: 11
QuoteOriginally posted by rawr Quote
I've taken a few thousand shots with my K200D and only seen this two times, thankfully.
These purple areas seem to be reflections coulered because of the coating not noise like in the TO's pictures.

Last edited by Darky; 07-20-2009 at 05:59 AM.
07-20-2009, 02:53 AM   #11
Inactive Account




Join Date: Jul 2009
Location: Brisbane, Australia
Photos: Gallery
Posts: 87
It's disapointing to hear that there are problems with your Pentax. Aside from the purple streaks the photos look great. Good job.
07-20-2009, 03:19 AM   #12
Pentaxian




Join Date: Jun 2009
Location: GMT +10
Photos: Albums
Posts: 10,576
QuoteOriginally posted by Darky Quote
These purple areas seems to be reflections coulered because of the coating not noise like in the TO's pictures.
You may be right. I will have to try to replicate this behaviour. Probably it is not a sensor issue.
07-20-2009, 03:56 AM   #13
Veteran Member




Join Date: Jan 2008
Location: Ste-Anne des Plaines, Qc., Canada
Posts: 2,014
I sometimes find the same happening with my K20D at high ISO. Since I more or less know it can happen in some situations, I try to avoid those situations. It's not a cure, but when you're aware of a problem, you can always try to work around it.
07-20-2009, 06:26 AM   #14
Veteran Member




Join Date: Mar 2007
Location: Boston, PRofMA
Photos: Albums
Posts: 3,053
QuoteOriginally posted by Darky Quote
That noise is called amplifier-noise...
ditto. The Nikons have this issue as well.

rawr's shots are something else though. Amp noise happens only at the edges...
07-20-2009, 10:59 AM   #15
Veteran Member
mtroute's Avatar

Join Date: Jun 2009
Location: Portland OR
Posts: 532
Original Poster
So what I am hearing is that there is no fix for the problem and that it is inherent in digital SLR's?
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
aperture, camera, dslr, exposures, iso, light, lights, location, photography, shutter
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
The K7 and long exposures pentaxmz Pentax DSLR Discussion 154 07-14-2010 06:53 PM
Nature Long exposures at the beach ismaelg Post Your Photos! 8 04-20-2010 10:39 PM
Cityscape Long Exposures attack11 Post Your Photos! 6 01-20-2010 01:49 PM
Long exposures. blwnhr Post Your Photos! 12 08-05-2008 03:36 AM
Strange noise with long exposures? silence2-38554 Pentax DSLR Discussion 8 07-02-2008 04:59 PM



All times are GMT -7. The time now is 03:29 PM. | See also: NikonForums.com, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top